A number of pneumatically operated devices have been developed for use in driving fasteners, such as staples and nails, into workpieces. These tools typically include an engine, a triggering system, and a head valve for controlling the flow of air to the engine. The engine generally includes a piston that is housed in a liner or sleeve, wherein the piston is coupled to a rod that extends through the liner and out of the nose of the tool. The triggering system controls the flow of compressed air to the main valve. The main valve is normally open to the atmosphere. When the triggering system is actuated, the main valve opens, simultaneously closing the path to the atmosphere and venting high pressure air that will act against the piston. The piston is pushed so that the rod that is attached thereto will apply a force to a fastener and thereby drive the fastener into a workpiece. When the triggering system is reset, or unactuated, the main valve closes, reopening the path to the atmosphere. The high pressure air that is over the piston is exhausted, allowing a charge of high pressure air that had been compressed by the movement of the piston to act against the opposite side of the piston to push it to its returned position.
Despite the wide spread use of such tools, several drawbacks have been noted. One such drawback concerns the main valve in that it adds a significant amount of weight and length to the tool. Another drawback concerns the mechanism by which the magazine assembly is mounted to the tool.